1. Field of the Invention
The present invention relates to a variable valve gear for an internal combustion engine, capable of changing the lift and the opening and closing timings of an intake valve.
2. Description of the Related Art
Conventionally, a variable valve lift mechanism for changing the lifts of intake and exhaust valves and a variable valve timing mechanism for changing the opening and closing timings (phases) of the valves are known as variable valve gears for internal combustion engines. An increasing number of modern internal combustion engines are equipped with both of these mechanisms in order to further improve the fuel efficiency and output performance.
In one such internal combustion engine provided with both the variable valve lift mechanism and the variable valve timing mechanism, a piston may interfere with the intake or exhaust valve near its top dead center when the lift or the opening and closing timings are considerably changed, if the two mechanisms are only combined.
Accordingly, a technique has been developed in which the operations of the variable valve lift and timing mechanisms are regulated lest the intake and exhaust valves interfere with the piston (Jpn. Pat. Appln. KOKAI Publication No. 2008-115779). According to this patent document, regulation means for regulating the change of the lift by the lift mechanism is provided in combination with regulation means for regulating the change of the valve-opening and closing timings by the timing mechanism. By these regulation means, the opening and closing timings are regulated based on the lift, or the lift is regulated based on the timings.
In the technique described in the above patent document, however, both the variable valve timing and lift mechanisms need to be each provided with the separate regulation means, so that the entire structure is complicated. If an attempt is made to continuously secure a high lift in accordance with the opening and closing timings, the variable valve timing and lift mechanisms should be cooperatively subjected to regulatory control. Thus, the control is inevitably complicated.